This invention relates generally to devices for measuring torque applied to a turning shaft and, more particularly, to devices for measuring torque applied to a steering column of a vehicle through a steering wheel.
Conventionally, a steering column is designed as a tubular element, fixed to the body of a vehicle under the instrument panel, that guides and supports a transmission shaft connected to the steering wheel. The steering wheel is then a manual control component, connected to the steered wheels and used by the driver for steering the vehicle.
The invention also concerns decoupled steering columns. In contrast to conventional steering columns, decoupled steering columns are not connected with a steering box transforming the circular movement of the steering wheel into angular displacement of the drop arm, that causes steering of the wheels. Quite the reverse, with decoupled steering there is no direct mechanical connection between the steering wheel and the wheels resting on the ground, whether the vehicle is real or belongs to a simulation system. This simulation can have the goal of games, in connection with training in automobile driving schools or even in connection with an interactive driving simulation for the needs of automobile manufacturers.
In such simulators, the interpretation of force at the steering wheel as a result of a mechanism generating a resisting torque on the steering wheel according to the type of vehicle to be simulated, which may or may not be equipped with power-assisted steering, must take into account the conditions to be recreated. The measurement of the torque applied to the steering wheel is consequently essential for ensuring good simulation in real time.
The measurement of the torque on the shaft of the steering wheel is also very important in power steering or power-assisted steering. In fact, the triggering of the assistance particularly depends on the torque applied to the steering wheel by the driver. The device for measuring the torque used in power steering produces a signal indicative of steering torque exerted by the driver on the steering wheel, and therefore on the transmission shaft of the steering column of the vehicle. This signal is conventionally addressed at a steering assistance computer that triggers the assistance by controlling, for example, an electric motor, in the case of electric power steering.
Measuring devices of the torque applied to the turning shaft are already known, and consist of a torsion bar in which an output signal is the analog type that is proportional to the magnetic field. For example, the detection of the angular displacement of two magnetic field generators in relation to detecting devices makes it possible to deliver an analog signal proportional to the torque applied. This type of analog magnetic technology has a number of drawbacks, in particular regarding the control of the air gap and the temperature balance of the magnetic field.
Within the scope of torque measuring devices of the prior art, the control of the air gap and drifts in temperature complicate the assembly because of the number of mechanical parts to be assembled and the precise placement of the magnetic transitions in relation to the detecting devices, which requires a phase for calibrating and regulating during assembly of the device. Furthermore, torque measuring devices of the prior art do not integrate bearings necessary for rotation of the turning shaft, which make the shaft and torque measuring device more complex to assemble.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one of more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is accomplished by providing a device for measuring torque applied to a turning shaft, the device comprising a test body that is deformable with torsion upon application of torque to the shaft and first and second bearings. Each bearing has a fixed collar, a turning collar, and rolling bodies arranged between them, the turning collar of the first bearing being connected with the test body near a first end of the test body, the turning collar of the second bearing being connected with the test body near a second end of the test body. The first and second bearings each are equipped with a digital device for determining angular position of the turning collar in relation to the fixed collar, with the digital devices including an annular means for generating magnetic pulses, mounted for turning jointly with the turning collar, and a fixed magnetic sensor for detecting the magnetic pulses and for delivering digital signals. An electronic means for processing digital signals from the magnetic sensors to determine the angular position of the annular means. A comparison device compares digital signals derived, respectively, from each of the electronic means to ascertain the torque applied to the turning shaft.
According to a second aspect of the invention, this is accomplished by providing a module for measuring torque applied to a turning shaft, with the module consisting of a device such as that described above and a means of connecting the module with, respectively, two parts of the turning shaft, with the turning shaft lacking a test body.
According to a third aspect of the invention, this is accomplished by providing a module for measuring torque applied to a turning shaft, with the module comprising a device such as that described above and a means of connecting the module with, respectively, one end of the turning shaft and the component applying the torque, with the turning shaft lacking a test body.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying